Wavefront aberration is an importance parameter in depicting properties of a small-aberration imaging optical system. Wavefront aberration of a high quality microscopic objective or a spatial telescope needs to be smaller than λ/4 PV or λ/14 RMS (where λ is an operating wavelength, and RMS is a root mean square value). Wavefront aberration of a deep UV lithographic projection lens needs to be in a few nm RMS, while that of an EUV needs to be less than 1 nm RMS, which demands for wavefront aberration techniques.
China Patent Application No. 201310126148.5A to Tang et al. discloses a point diffraction interferometric wavefront aberration measuring device and a detecting method where two standard spherical waves are generated on an object plane of a measured optical system, and the light intensity, polarization states, and optical path difference thereof are adjustable for producing high interference visibility, and the measured results are able to eliminate the system errors. Nevertheless, in the case the photoelectric sensor in the image wavefront detection unit is just a two-dimensional detector without replaceable optical lens, the technique results in a loss of interference data in certain regions of the periphery of the numerical aperture of the measured optical system, thus elimination of the system error for a complete numerical aperture is impossible. Additionally, the measuring procedure is too complex. Moreover, when the wavefront aberration of the measured optical system is very small, the technical system error of the current technology is far greater than the wavefront aberration of the measured optical system. Thus, the detection result is greatly influenced by the random noise of the system, and multiple measurements are required and then averaged to increase detection precision.